Explosive residue analysis : evaluation and optimisation of sampling, storage and cleanup protocols

Abstract

For the detection and identification of explosive residues, surfaces of interest are typically sampled by swabbing or solvent wash. The current use of sequential swabbing protocols that separately target organic and inorganic compounds is under threat due to the increased use of improvised organic/inorganic explosive mixtures. An optimised swabbing procedure, using commercially available skin cleansing alcohol wipes, was developed to maximize the collection of both organic and inorganic explosive residues in a single step. Using six representative compounds (TNT,RDX,PETN,TATP, ammonium nitrate, and sodium chlorate) and four different substrates (glass, plastic, aluminium foil and laminate),the collection efficiency of the alcohol wipes was compared to the results obtained using conventional cotton swabs, polyester swabs, and a direct solvent wash (used as a control). The alcohol wipes demonstrated better overall performance in the recovery of both the organic and inorganic compounds from all test surfaces. The compositions of a mixture of three organic solvents (acetone, acetonitrile and methanol) and water for a single-step solvent extraction of both organic and inorganic representative compounds from the alcohol wipes was investigated. In addition, the study included the evaluation and optimisation of a subsequent solid-phase extraction (SPE) clean-up procedure for the wipes extracts utilising several solid-phase extraction cartridges (both commercially available and prepared in-house). The application of a polyester alcohol wipe as a universal swab, followed by extraction with 60% v/v methanol/water and clean-up with a Nexus SPE cartridge, was proposed as the final optimised protocol for the combined recovery and clean-up of organic and inorganic explosive residues. The stability of the six representative compounds on polyester wipes and in 60% v/v methanol/water extracts, stored over 30 days in clear and amber glass vials at three different temperatures, was assessed in order to establish storage recommendations in conjunction with the final proposed protocol. The retention of all six target compounds on a glass surface at two different storage temperatures was included for an estimation of the maximum time that the explosive material could still be detected and recovered from a stored exhibit. The results from the stability study suggested that, after sampling, the wipes should be stored in a dark and low temperature environment. Also, after processing using the proposed protocol, the extracts should be stored in a similar fashion. The results from the retention study of the six target compounds on the glass substrate suggested that exhibits should be stored at the lowest temperature possible to minimise the loss of any TNT or TATP (or similar target compounds) that might be contained within the sample.

Date of Award	2011
Original language	English
Supervisor	Christopher Lennard (Supervisor) & Dennis McNevin (Supervisor)